1. Field
Example embodiments herein relate to a membrane, a method of manufacturing the same, and a composite membrane including the same.
2. Description of the Related Art
To acquire fresh water or gray water from sea water or sewage and waste water, floating or dissolved components should be removed in conformity with the standards for drinking water. At present, reverse osmosis is conventionally used as a water treatment method for desalinating or making gray water out of sea water or sewage and waste water.
According to the water treatment method using a reverse osmotic membrane, a pressure corresponding to an osmotic pressure caused by the dissolved component is applied to the raw water to separate a dissolved component, such as a base (NaCl), from water. For example, the concentration of the base dissolved in sea water ranges from about 30,000 to about 45,000 ppm and the osmotic pressure caused from the concentration ranges from about 20 to about 30 atm. As a result, a pressure of about 20 to 30 atm or higher is applied to the raw water to produce fresh water from the raw water. Typically, energy in the amount of about 6 to about 10 kW/m3 is required to produce about 1 m3 of fresh water from sea water.
An energy recollection device has been developed and applied in an attempt to save the energy consumed during a reverse osmosis process. However, in this case, about 3 kW/m3 of energy is required to drive a motor of a high-pressure pump.
To resolve the problem, a water treatment process based on forward osmosis has been suggested as an alternative. The forward osmosis process is relatively economical compared with the reverse osmosis process, because the forward osmosis process does not require pressure but uses a natural osmosis phenomenon. Researchers have been studying the development of the forward osmosis process.
In the forward osmosis process, the chemical characteristics of a membrane are important as is the structure of the membrane. In the reverse osmosis process, since the water passing through the membrane is transported by pressure, the chemical characteristics of the membrane affects the water flux of the membrane less.
However, in the forward osmosis process, the water is spontaneously permeated to the membrane by the osmotic pressure difference, so the hydrophilicity of the membrane significantly affects the water flux. Accordingly, the hydrophilic degree of a polymer for the membrane may significantly affect the water flux of the membrane.
Accordingly, it may be favorable for the membrane to be fabricated using a hydrophilic polymer in view of the water flux of the membrane, but this may increase the thickness of a skin layer due to the hydrophilicity of the polymer when the membrane is fabricated according to a non-solvent induced phase separation (NIPS), which is a conventionally used method.
When the skin layer is thicker, the structural factor of the membrane is increased, which may decrease the water flux.